Spheres such as steel balls and ceramic balls, which are used for ball bearings and the like, are manufactured by a sphere polishing device. The sphere polishing device includes a sphere size measuring device for measuring the size of the spheres, thus some spheres in the course of processing are extracted as object spheres and the sizes thereof are measured by the sphere size measuring device. Processing operations of the sphere polishing device are controlled according to diameters of the measured spheres. For example, Patent Document 1 discloses that the spheres are processed in consideration of the efficiency till the diameter of the object sphere reaches a predetermined value, and that after the diameter of the object sphere reaches the predetermined value, then the spheres are processed in consideration of the quality.
Patent Document 2 discloses a sphere size measuring device including a posture changing mechanism for changing the posture of the object sphere. Since the average diameter is calculated based on measured values at a plurality of positions, the measurement accuracy can be improved.